Myopia (nearsightedness) is on the rise around the world and in the United States. It affects tens-of-millions of Americans and, in progressive forms, is a leading cause of blindness. Earlier research with humans and experimental animal models has shown that the postnatal development of the eye and its refractive state involves a combination of genetic and visual factors. The rising incidence of myopia in humans has been associated with increases in literacy and levels of education, although the nature of the relationship is unclear and predicting who will become myopic is difficult. Research using animal models has established that visual stimuli related to retinal defocus are used to regulate eye growth and refractive state. The principal aim of this proposal is to explore the spatial and temporal integration of the visual signal that drives eye growth. We will examine how eye shape, the optical quality of the eye, and accommodation interact and may affect that signal. An additional line of investigation will examine how visual acuity is affected by experimental manipulations that alter eye growth and refractive state. The specific aims and questions being asked in this proposal are the following: Aim 1. Characterize changes in eye shape, peripheral refraction, and off-axis optics during experimentally-induced refractive errors. Do differences in eye shape, and the peripheral refractive states associated with them, make the eye more susceptible to developing a refractive error? How, in turn, is eye shape affected by the development of refractive errors? Aim 2. Examine the spatial integration of peripheral retinal defocus for the regulation of eye size and refractive state. Is refractive state in the retinal periphery important for the visual control of eye growth and the development of refractive error? Is there local eye growth in the primate, and can it influence axial length and refractive state on-axis? Aim 3. Examine the effects of brief periods of controlled focus on the regulation of eye size and refractive state. How does the primate eye temporally integrate visual defocus signals that affect eye growth? How does emmetropization function given that accommodation alters retinal defocus from moment-to-moment and potentially removes hyperopic defocus cues? Aim 4. Correlate changes in visual acuity with induced changes in eye growth and refractive state. Do lens-induced refractive changes affect visual acuity in marmosets? Can compensation for visually induced defocus take place without changes in visual acuity?